There is a great interview up at CBR featuring Grant Morrison, Tim Kring, Mike Mignola, and Johnathan Lethem. Go check it out.
Morrison said superheroes are representative of certain qualities and as such they need to be allegorical of other concepts in order to appeal to more adult readers. As an example, Morrison explained that when he was young he liked The Flash as drawn by Carmine Infantino simply because his bright yellow boots looked so cool due to their “awesome huge treads.” Now that Morrison is older, boot design isn’t enough to make the character appeal to him. Now Morrison likes The Flash because he feels he is representative of urban living and urban culture due to his speed. Morrison explained that lives of superheroes are huge cosmic version of the way human beings live, and that if they were not based in the lives of ordinary humans, they may not have an appeal.
I love that man so much.